Search found 35 matches

by bobtidey
Sat Jun 06, 2020 11:44 am
Forum: Hardware
Topic: ESP32 powering a solenoid
Replies: 11
Views: 312

Re: ESP32 powering a solenoid

I think that even for the 2n2222A version it is hard to come up with a worst case design that provides sufficient Ib to saturate and yet doesn't potentially try to draw more than 40mA from a GPIO. 2n2222A max Vbe Sat @ 500mA Ic 2V might be a bit less at 300mA but not actually specified Assume GPIO V...
by bobtidey
Fri Jun 05, 2020 8:43 pm
Forum: Hardware
Topic: ESP32 powering a solenoid
Replies: 11
Views: 312

Re: ESP32 powering a solenoid

Just to amplify further why I think trying to exploit potential 40mA capability of a GPIO would be a bad idea. 1 Vbe sat of a 2n2222A could be 2.0V 2 Vo of a GPIO at 40mA could drop to 2.6V 3 So to guarantee 30mA Ib what base resistor would you use? 4. Then under typical conditions where GPIO might ...
by bobtidey
Fri Jun 05, 2020 8:27 pm
Forum: Hardware
Topic: ESP32 powering a solenoid
Replies: 11
Views: 312

Re: ESP32 powering a solenoid

When using bipolar transistors for switching you do not use the current gain (beta) to determine appropriate base current. That parameter is specified when the transistor is in its linear region with a significant Vce. Gain drops off dramatically as Vce falls. The normal 'rule' for switching is that...
by bobtidey
Thu Jun 04, 2020 8:53 pm
Forum: Hardware
Topic: ESP32 powering a solenoid
Replies: 11
Views: 312

Re: ESP32 powering a solenoid

Using a bipolar transistor like a 2n2222 is not a great idea for switching the current to the solenoid. For a 300mA solenoid you would need to feed about 30mA into the base of the transistor to saturate it (switch it hard on). That is to much for a GPIO pin. You could use a darlington transistor lik...
by bobtidey
Sat May 09, 2020 8:52 pm
Forum: Hardware
Topic: GPIO drive strength.
Replies: 6
Views: 2106

Re: GPIO drive strength.

As has been pointed out a series gate resistor does very little when using a MOSFET driver. The only possible benefit would be to add a degree of protection to the GPIO pin if there was some catastrophic failure in the MOSFET device. These tend to be very reliable devices and I do not add a series r...
by bobtidey
Tue Feb 25, 2020 11:21 am
Forum: ESP32 Arduino
Topic: ESP32-CAM Problem with not enough pins
Replies: 8
Views: 3328

Re: ESP32-CAM Problem with not enough pins

You can use the TXD and RXD pins as GPIO.

Obviously they are not operational during a flash upload operation which may mean swapping wires to do uploads but if you use OTA then that doesn't matter after the first flash.

Using RXD doesn't affect any serial debug print but using TXD will.
by bobtidey
Mon Feb 17, 2020 8:56 am
Forum: ESP32 Arduino
Topic: SAMPLING AUDIO - How to handle large data?
Replies: 6
Views: 1619

Re: SAMPLING AUDIO - How to handle large data?

If you use an esp32 module with 4MByte PSRAM (e.g. WROVER) then you can store your whole capture in a buffer before writing out to file.
by bobtidey
Tue Feb 04, 2020 11:55 am
Forum: ESP32 Arduino
Topic: ESP32-CAM does not boot with DS18B20 on GPIO14
Replies: 4
Views: 951

Re: ESP32-CAM does not boot with DS18B20 on GPIO14

I don't know why GPIO14 would affect the boot unless it is something to do with the camera software. Maybe try it with a minimal sketch to see if that boots OK with GPIO14 pulled up. On my camera app I do use the SD card so there is little IO free. I use RXD as GPIO3 pin; just use pinMode in setup.....
by bobtidey
Tue Dec 31, 2019 4:01 pm
Forum: Hardware
Topic: ESP32-CAM Power Issue - Works with 3.3V but not with 5V
Replies: 2
Views: 1805

Re: ESP32-CAM Power Issue - Works with 3.3V but not with 5V

Everything on the board runs from the 3.3V rail. There are 2.8V and 1.2V rails but these are derived from the 3.3V rail. The only thing the 5V connection does is connect to a 1117 linear regulator to provide the 3.3V. So if the board works fine when fed directly from 3.3V then there seems to be only...

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